1. Field of the Invention
The present invention relates to an optical information accessing system for an optical disk including a plurality of sectors.
2. Description of the Related Art
In an optical disk, a plurality of helical tracks are formed thereon, and each of the tracks includes a plurality of sectors each having a sector mark showing a start thereof. Therefore, in order to perform a read operation upon a specific sector, a sector mark is detected from data read from the optical disk, and a sector mark detection signal is generated within a definite time period, i.e., a so-called window defined by a window signal. Then, the read operation is carried out by the sector mark detection signal as a sector initiation signal. On the other hand, even when such a sector mark detection signal is not generated, the read operation is carried out by a sector mark interpolation signal which is generated in synchronization with sector mark detection signals which have been generated.
In the above-mentioned prior art optical disk, however, when no sector mark detection signal is generated for a long time, it is determined that the timing of detection of sector marks is remarkably shifted from the timing of the window signal, so that the window signal is always made active, i.e., in a full open state. Then, the window signal is made inactive when the next sector mark detection signal is generated. As a result, two sector initiation signals, i.e., one sector mark detection signal and one sector mark interpolation signal may be generated for one sector. In this case, for example, a jump back control-is carried out by counting the sector initiation signals and therefore, the jump back control is erroneously carried out. This will be explained later in detail.